The stem has now been set up and braced in position, and a series of heavy timbers that butt up to the aft end of the stem have been attached. These big timbers are called ‘Knightheads.’ You can see them attached to the stem in this photo with yellow straps.

Once the knightheads are through-bolted, the final stem member is installed. This is the stem knee, and it’s made of one of the toughest woods known: live oak.

Live oak is a favored wood for curved boat parts. It’s incredibly tough, primarily because it has interlocked grain. If you tried to split a live oak log with an axe, you’d get nowhere. The grain doesn’t run in nice, parallel lines that make for clean splitting. Instead, it swirls and curves around. This means live oak doesn’t fracture along its grain when stressed. It’s also a very heavy, dense wood. The USS Constitution was framed and planked in live oak, and was nicknamed “Old Ironsides” because of it’s ability to withstand cannon attacks.

We don’t anticipate cannon attacks, so we’re just using live oak in high-stress areas, like the stem knee.

Bolting all these parts together can be quite a trick. The best way to hold all these parts together is with long custom bolts that go from the outside of the stem to the inside of the stem knee. That’s a lot of wood to traverse,

and there’s always the danger that your bit will wander a bit while you’re drilling and end up somewhere you don’t want it to. In the worst case scenario, you poke out the side of the piece you were drilling into.

The underside of the stem is not very wide,

and neither is the top face of the knee. If you start drilling just a fraction of a degree out of line with the center of the stem, you can end up with a hole that’s way, way off center by the time you come out of the knee.

The guys take a lot of time to set these drilling operations up, and they bring out the big guns for this job: the Milwaukee Hole Hog.

This drill has torque like a freight train, and it’s the tool of choice when drilling long holes through tough woods.

You can’t usually find drill bits that are long enough to make holes like this, so the guys take a regular bit and very carefully weld an extension rod to the bit.

Some of these holes are 2’ or longer.

The end result:

Not bad at all. You can see that the lower hole is just slightly off to starboard, but that’s just academic.

The guys spent some time working out the trunnels for the boat this month. The trunnels (or “tree nails”) as you may recall are used to pin parts together. The original boat’s planking was held on almost entirely by trunnels.

Trunnels should fit very tightly, so it’s important to have them be a consistent thickness, and have the holes that they go into be equally precise. One way to make sure that your trunnel absolutely locks into place is to use dry wood. Once the wood gets a little moist it will expand and lock into its hole. To this end, the crew built a drying box to gently heat the trunnels and keep them bone dry prior to installation.

They also made a special driving cap that goes over the top of the trunnel and keeps the head from being smashed out when the trunnel is driven into its hole. Here are some pieces being tested for fit, with the driving cap on one of them.

And these are some of the trunnels that came out of the boat. Keep in mind that these were installed around 1884.

Not bad.

You can see the slot at the end of each of these trunnels. There’s one at each end. The way that these parts hold is that a wedge is driven into these slots once the trunnel is seated in its hole. The wedge pries out the last bit of the trunnel hard against the hole wall, and this little flare jams the trunnel in place. It’s like a wooden rivet.

The slot at one end is cut with a band saw, the other slot is made after the trunnel is driven through the part. The excess trunnel coming out of the hole is cut to leave about an inch protruding, and the slot is made with a tool called a fro.

The guys didn’t have a fro on hand, so Eric forged one.

A little work on the grinding wheel to get the shape right

It looks like a barber’s straight razor,

but it’s not nearly as delicate or sharp.

Final product

The job of the fro is to split the end of the trunnel like you see Claes doing here.

With the end split, it’s easy to drive a wedge into the trunnel’s end.

With the wedge driven in, the trunnel is cut off flush. You can see the wedge locked into the end.

Comments

One Response to “Progress through July 2010”

Great coverage of the trunnel action! Some of those old ones pictured may not date from 1885. The most ancient ones are not round (made on a trunnel machine), but flat sided (apparently drawn with a draw knife) and thinner in diameter. Those are the REAL oldies. Some of these pictured may havea been driven as late as the 1970’s when a crewmember and I replaced some topside planking on the starboard quarter in Gloucester, Mass. You guys are doing fantastic work! Even making the tools…. We used what we could find, i.e., a simple wood chisel, for a fro…. But the trunnels held.